Tripod type constant velocity joint

ABSTRACT

A tripod type constant velocity joint comprising a hollow cylindrical housing fixed to the end of a first rotary shaft and formed at the inner peripheral surface thereof with axially extending recessed grooves opened at one axial end and located at circumferentially trisectional positions on the inner peripheral surface, a tripod consisting of a boss fixed to the end of a second rotary shaft, and end-spherical trunnion journals radially projecting from circumferentially trisectional positions on the boss, a roller assemblies each consisting of an inner roller swingably fitted at the inner peripheral surface thereof on the spherical outer peripheral surface of the trunnion journal, and an outer roller supported for rotation and axial movement on the outer peripheral surface of the inner roller through needle rollers, wherein the outer rollers are received in the recessed grooves in the housing and are rollable axially of the housing, each recessed groove consists of guide surfaces contacting the outer peripheral surface of the outer roller and subjected to loads, and guide shoulder surfaces for guiding the outer roller axially of the housing, and only the side of the outer diameter of said boss associated with the end of the second rotary shaft is heavily chamfered. A relief is locally formed along the forged parting line of the trunnion journal. The root of the tripod journal is of non-circular cross-section in which the diameter as measured circumferentially of the joint is larger than the diameter as measured axially of the joint.

BACKGROUND ART

[0001] The present invention relates to a tripod type constant velocityjoint used for transmission of a rotary force between rotary shaftsincorporated in the driving system, for example, of an automobile andnon-linearly existing therein.

[0002] Tripod type constant velocity joints are in wide use as a kind ofconstant velocity joint to be incorporated in the driving systems ofautomobiles. For example, Japanese Patent Laid-Open Publication Sho62-233522 discloses a tripod type constant velocity joint 1 as shown inFIGS. 15 and 16. This tripod type constant velocity joint 1 comprises ahollow cylindrical housing 3 fixed to the end of a first rotary shaft 2,such as a driving shaft, and a tripod 5 fixed to the end of a secondrotary shaft 4, such as the rotary shaft on the wheel side.

[0003] The inner peripheral surface of the housing 3 is formed, atcircumferentially trisectional positions, with recessed grooves 6extending axially of the housing 3. On the other hand, the tripod 5comprises a boss 7 to be fixed to the end of the second rotary shaft 4,and columnar trunnion journals 8 radially projecting from thecircumferential trisectional positions on the boss 7. Each trunnionjournal 8 supports a roller 9 for rotation and more or less axialdisplacement through needle rollers 10. And these rollers 9 are fittedin the recessed grooves 6 in the housing 3, thereby constituting thetripod type constant velocity joint 1. In addition, a pair of guidesurfaces 6 a defining each recessed groove 6 are each an arcuatelyrecessed surface, and each roller 9 is supported for rolling andswinging between these guide surfaces 6 a.

[0004] During the use of the tripod type constant velocity joint 1constructed as described above, when, for example, the first rotaryshaft 2 is rotated, its rotary force is transmitted from the housing 3to the boss 7 of the tripod 5 successively through the rollers 9, needlerollers 10, and trunnion journals 8, rotating the second rotary shaft 4.Further, when the center axis of the first rotary shaft 2 is out ofalignment with the center axis of the second rotary shaft 4, that is,when the tripod type constant velocity joint 1 takes an operating angle,with the rotation of the two rotary shafts 2 and 4, each trunnionjournal 8 is displaced in a direction to swing around the axis of thetripod 5 with respect to the guide surfaces 6 a of the correspondingrecessed groove 6, as shown in FIGS. 15 and 16. At this time, the roller9 supported by each trunnion journal 8 rolls on the guide surfaces 6 aof the recessed groove 6 while being displaced axially of the trunnionjournal 8. These movements secure equality of velocity between the firstand second rotary shafts 2 and 4.

[0005] In the case of the tripod type constant velocity joint 1constructed to act in the manner described above, when the first andsecond rotary shafts 2 and 4 are rotated with an operating angle taken,each roller 9 performs a complicated motion. That is, each roller 9moves along the guide surfaces 6 a while changing its direction axiallyof the housing 3 and is displaced axially of the trunnion journal 8.When each roller performs such complicated motion, relative displacementbetween the outer periphery surface of each roller 9 and the guidesurfaces 6 a is not necessarily smoothly effected, so that relativelylarge friction is generated between these surfaces. As a result, in thecase of the tripod type constant velocity joint of the constructionshown in FIGS. 15 and 16, a tertiary axial force is generated perrevolution. And it is known that a vibration called shudder is generatedin remarkable cases as when it is incorporated into an automobile totransmit a large torque with a large operating angle taken.

[0006] As measures against the above problem, French Patent No. 2752890discloses a construction as shown in FIG. 17a and Japanese PatentLaid-Open Publication Heisei 3-172619 discloses a construction as shownin FIG. 19. The construction of FIG. 17a is such that a roller assembly(inner and outer rollers relatively rotatable through needle rollers) isparallelly guided in a recessed groove in the housing and such thatcentering and swinging are made possible between the spherical innerperipheral surface of the inner roller and the spherical trunnionjournal, and spherical fitting is ensured in that the generating line ofthe outer peripheral surface of the spherical trunnion journal is an archaving a radius of curvature, r_(T), smaller than the radius (A/2) ofthe trunnion journal. In this case, the major diameter of a contactellipse generated under a load torque between the inner roller sphericalinner peripheral surface and the spherical trunnion journal becomeslonger. Increasing a spherical surface clearance {(C-A)/2} makesspherical fitting possible without having to make the radius ofcurvature, r_(T), smaller than A/2. In that case, however, not only doesthe rotation-directional play become larger but also the contact areabecomes smaller, resulting in a disadvantage leading to rotationdurability decreasing with increasing contact surface pressure.

[0007] With the construction of FIG. 19, since a torque load is imposedbetween the cylindrical inner peripheral surface 20 of the inner rollerand the spherical trunnion journal 8, the contact surface area furtherdecreases, resulting in a disadvantage leading to rotation durabilitydecreasing with increasing contact surface pressure. Further, the width(corresponding to the contact ellipse minor diameter) of the contactsurface further decreases and the circumferential contact lengthcorresponding to the major diameter further increases. The contactsurface pressure is also high.

[0008] In these prior art tripod type constant velocity joints, a swingslip that takes place on the contact ellipse due to the swing of thetrunnion journal when the joint is rotating under a load with anoperating angle taken acts, as shown in FIG. 18, as a spin momenttending to change the rolling direction of the roller assembly, so thatthe roller assembly has its direction changed until it contacts theguide surfaces of the recessed groove in the housing, and the contactforce becomes greater. Further, since it is no longer parallel with therecessed groove in the housing, it is thought that smooth rolling isimpeded and the rolling resistance cannot be fully reduced.

[0009] A main object of the invention is to provide a tripod typeconstant velocity joint that has solved the above problems. That is, theinvention is intended to provide a tripod type constant velocity jointwherein while holding small the clearance between the sphericallysurface-fitting inner roller and spherical trunnion journal, that is,holding the rotation-directional play small, spherical fitting (surfacepressure reduced) is made possible and the contact ellipse majordiameter is reduced so as to keep small the spin moment generated by theswing of the trunnion journal, so as to minimize the rolling resistancein the roller assembly during the rolling with an operating angle taken,thereby ensuring the coexistence of reduced shudder and high durabilitywhen the joint is assembled to an automobile.

DISCLOSURE OF THE INVENTION

[0010] According to an embodiment of the invention, a tripod typeconstant velocity joint comprises a hollow cylindrical housing fixed tothe end of a first rotary shaft and formed with axially extendingrecessed grooves opened at one axial end and located atcircumferentially trisectional positions on the inner peripheralsurface, a tripod consisting of a boss fixed to the end of a secondrotary shaft, and end-spherical trunnion journals radially projectingfrom circumferentially trisectional positions on the boss, rollerassemblies each consisting of an inner roller swingably fitted at theinner peripheral surface thereof on the spherical outer peripheralsurface of the trunnion journal, and an outer roller supported forrotation and axial movement on the outer peripheral surface of the innerroller through needle rollers, wherein the outer rollers are received inthe recessed grooves in the housing and are rollable axially of thehousing, each recessed groove consists of guide surfaces contacting theouter peripheral surface of the outer roller and subjected to loads, andguide shoulder surfaces for guiding the outer roller axially of thehousing, and only the side of the outer diameter of said boss associatedwith the end of the second rotary shaft is heavily chamfered. Thisembodiment is arranged so that during assemblage by tilting the rolleruntil the projected shorter radius of the trunnion journal (in adirection at right angles with the load-subjected side) is reduced tonot more than its inner diameter at its end on the inner roller fittingside, the roller does not interfere with the boss of the tripod (journalunderhead). Since torque transmission between the tripod and the secondrotary shaft is effected mostly by the second rotary shaft non-end sidein the boss, heavily chamfering the boss at the second rotary shaft enddoes not lead to a lowering in the boss strength. Mounting this tripodtype constant velocity joint on a vehicle makes it possible to reducethe vibration of the vehicle and to ensure coexistence of high strengthand durability.

[0011] The load-subjected position (contact ellipse center position) onthe spherical outer peripheral surface of the trunnion journal may beprovided with a flat surface or dent of suitable size. The flat surfaceor dent is located in the region inwardly receding from the sphericalouter peripheral surface of the trunnion journal and has an optionalsize within a range where the contact area decreases, for example, to ⅕of the contact area due to spherical fitting without such flat surfaceor dent. There is almost no relative displacement in the center of theregion of spherical contact between the trunnion journal and the innerroller, in which poor lubrication could occur, and smearing measures canbe taken by providing said flat surface or dent so as to avoid contactin said region.

[0012] At least one end of the inner peripheral surface of the outerroller may be integrally formed with a needle roller retainer. Thus, byforming the outer roller integrally with an inner needle roller retainerand an outer needle roller retainer, it is possible to constitute aroller assembly by only three elements, the inner roller, needle rollersand outer roller, reducing the number of parts. In this case, therelation Di<do can be established where Di is the inner diameter of thecylindrical inner peripheral surface of the outer roller at the jointinner diameter side end and do is the outer diameter of the innerroller. Adopting such arrangement makes it difficult for the outerroller to be detached from the inner roller in the state of the tripodkit (a unit consisting of the tripod and the roller assembly), makinghandling easy.

[0013] At least one end of the outer peripheral surface of the innerroller may be integrally formed with a needle roller retainer. Byforming the inner roller integrally with an inner needle roller retainerand an outer needle roller retainer, it is possible to constitute aroller assembly by only three elements, the inner roller, needle rollersand outer roller, reducing the number of parts. In this case, therelation Di<do can be established where do is the outer diameter of thecylindrical outer peripheral surface of the inner roller at the jointinner diameter side end and Di is the inner diameter of the outerroller. Adopting such arrangement makes it difficult for the outerroller to be detached from the inner roller in the state of the tripodkit, making handling easy.

[0014] According to another embodiment, a tripod type constant velocityjoint comprises a hollow cylindrical housing fixed to the end of a firstrotary shaft and formed with axially extending recessed grooves openedat one axial end and located at circumferentially trisectional positionson the inner peripheral surface, a tripod consisting of a boss fixed tothe end of a second rotary shaft, and end-spherical trunnion journalsradially projecting from circumferentially trisectional positions on theboss, roller assemblies each consisting of an inner roller swingablyfitted at the inner peripheral surface thereof on the spherical outerperipheral surface of the trunnion journal, and an outer rollersupported for rotation and axial movement on the outer peripheralsurface of the inner roller through needle rollers, wherein the outerrollers are received in the recessed grooves in the housing and arerollable axially of the housing, each recessed groove consists of guidesurfaces contacting the outer peripheral surface of the outer roller andsubjected to loads and guide shoulder surfaces for guiding the outerroller axially of the housing, and a relief is locally formed along theforged parting line of the trunnion journal, thereby receding theprotuberance of the forged parting line inwardly from the outerperipheral surface of the trunnion journal. Providing a relief resultsin the protuberance of the forged parting line not projecting beyond theouter peripheral surface of the trunnion journal, thus making itpossible to effect spherical fitting surface contact between the innerroller and the trunnion journal without the operation of removing theprotuberance of the forged parting line, and the surface pressurelowers. Therefore, it is possible to provide a tripod type constantvelocity joint ensuring the coexistence of reduced shudder with thejoint assembled to a vehicle, high durability and cost reduction.

[0015] The cross-section of the trunnion journal in the torque loadregion may be substantially double spherical. In that case, the partingline position on the trunnion journal recedes from the inner sphericalsurface of the inner roller toward the minor diameter side, so that arelief is formed without taking special measures. In a torque-loadedstate, the contact regions between the trunnion journal and the innerroller are located in two positions symmetrical with respect to theforged parting line of the trunnion journal, but their abutment occursin their spherical surfaces, so that there is no danger of edge loading.As a concrete embodiment of said substantially double spherical shape,an example may be mentioned in which the radius R of the doublespherical surface of the trunnion journal is set so that r/2<R<r where ris the radius of curvature of the spherical inner peripheral surface ofthe inner roller.

[0016] Let θ be the angle at which the roller assembly is tilted whenassembled to the trunnion journal. Then, by setting the maximum diameterφD of the trunnion journal (including the forged parting line) projectedin the direction of angle θ not more than the inner diameter φd of theinner roller on the insertion side, it is possible to assemble theroller assembly to the trunnion journal without elastically deformingthe inner roller during incorporation. Therefore, according to thisembodiment, it becomes possible to omit the forged parting line removingstep and the force fitting step required for assembling the rollerassembly to the trunnion journal. Further, a notch may be locally formedin the inner diameter of the inner roller on the insertion side, and thesetting may be such that φD₂<φd₂ where φd₂ is the inner diameter of thenotch and φD₂ is the maximum diameter of the trunnion journal (includingthe forged parting line) projected in the direction of angle θ.

[0017] The setting may be such that with θ₁ being the angle at which theroller assembly is about to separate from the trunnion journal, theroller assembly interferes with the rotary shaft when it is tilted up toan angle θ₂ (θ₂<θ₁) after the rotary shaft has been mounted in a tripodkit. Herein, a unit consisting of a tripod and roller assemblies istermed a tripod kit. Further, the term “rotary shaft” shall include notonly the rotary shaft itself but also a separate member, such as a stopring, attached to the rotary shaft. Employing such arrangement ensuresthat in the state of the unit consisting of the tripod and rollerassemblies, that is, tripod kit, the tripod is assembled to the secondrotary shaft, and once a stop ring is mounted, the inner rollerinterferes with the stop ring or the rotary shaft and cannot tilt up tothe angle θ₁ at which it separates from the trunnion journal, so thatthe tripod kit and the rotary shaft assume a unit handling state, whichgreatly facilitates handling.

[0018] According to another embodiment of the invention, a tripod typeconstant velocity joint comprises a hollow cylindrical housing fixed tothe end of a first rotary shaft and formed at the inner peripheralsurface thereof with axially extending recessed grooves opened at oneaxial end and located at circumferentially trisectional positions on theinner peripheral surface, a tripod consisting of a boss fixed to the endof a second rotary shaft, and end-spherical trunnion journals radiallyprojecting from circumferentially trisectional positions on the boss,roller assemblies each consisting of an inner roller swingably fitted atthe inner peripheral surface thereof on the spherical outer peripheralsurface of the trunnion journal, and an outer roller supported forrotation and axial movement on the outer periphery of the inner rollerthrough needle rollers, wherein the outer rollers are received in therecessed grooves in the housing and are rollable axially of the housing,each recessed groove consists of guide surfaces contacting the outerperipheral surface of the outer roller and subjected to loads, and guideshoulder surfaces for guiding the outer roller axially of the housing,it being arranged that when the roller assembly is to be assembled tothe trunnion journal, it is done so by tilting the roller assemblyaxially of the joint, the root of the tripod journal being ofnon-circular cross-section in which the diameter measuredcircumferentially of the joint is larger than the diameter measuredaxially of the joint. As for a non-circular shape in which the diametermeasured circumferentially of the joint is larger than the diametermeasured axially of the joint, there may be mentioned, for example, anelliptic shape with its minor axis directed axially of the joint.Assembling the roller assembly to the trunnion journal by tilting it ina plane including the direction of the axis of the joint makes itessential only that the interference-avoiding relief for assembling thejournal underhead and the roller to each other be present only on theside of the journal underhead as seen axially of the joint, so that theinterference-avoiding relief for assemblage on the side thereof as seencircumferentially of the joint becomes unnecessary. In the case of suchdesign specification, since there is no interference-avoiding relief inthe underhead circumferential position tending to be the maximum stressposition when subjected to torque load, strength improvement becomespossible and it is possible to provide a more compact joint.

[0019] These and other objects and arrangements of the invention willbecome more apparent from the following description to be given withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1a is a cross-sectional view of a tripod type constantvelocity joint showing an embodiment of the invention, and FIG. 1b is apartial enlarged view of FIG. 1a;

[0021]FIG. 2 is a longitudinal sectional view of the tripod typeconstant velocity joint of FIG. 1a;

[0022]FIG. 3 is an exploded sectional view of a tripod kit, illustratinghow to assemble a roller assembly to a trunnion journal;

[0023]FIGS. 4a-4 c are side views of the trunnion journal;

[0024]FIGS. 5a and 5 b, and FIGS. 6a and 6 b are sectional view of thetrunnion journal and the roller assembly;

[0025]FIG. 7a is a side view of the trunnion journal, FIG. 7b is across-sectional view of the trunnion journal, and FIG. 7c is an enlargedview of a forged parting line projection of FIG. 7b;

[0026]FIG. 8a is a side view of the trunnion journal, and FIG. 8b is across-sectional enlarged view of a contact region between the trunnionjournal and an inner roller;

[0027]FIG. 9a is a front view of the trunnion journal, FIG. 9b is a sideview of the trunnion journal, and FIG. 9c is an enlarged view of thearea c of FIG. 9a;

[0028]FIG. 10 is a cross-sectional diagram of the contact region betweenthe trunnion journal and the inner roller;

[0029]FIG. 11 is a sectional view of the tripod kit;

[0030]FIG. 12a is a front view of the tripod, and FIG. 12b is asectional view taken along the line b-b in FIG. 12a;

[0031]FIG. 13 is an exploded sectional view of a tripod kit similar tothat shown in FIG. 3;

[0032]FIG. 14a is a sectional view of the inner roller, and FIG. 14b isa view taken in the direction of arrow Y in FIG. 14a;

[0033]FIG. 15 is a perspective view of a tripod type constant velocityjoint, showing the prior art;

[0034]FIG. 16 is a longitudinal sectional view of the tripod typeconstant velocity joint of FIG. 15;

[0035]FIG. 17a is a partial sectional view showing the positionalrelation between the roller and the trunnion journal in the prior arttripod type constant velocity joint, and FIG. 17b is a cross-sectionalview of the trunnion journal in FIG. 17a;

[0036]FIG. 18 is a sectional view for explaining a spin moment generatedin the prior art tripod type constant velocity joint; and

[0037]FIG. 19 is a partial sectional view of another prior art tripodtype constant velocity joint.

BEST MODE FOR EMBODYING THE INVENTION

[0038] An embodiment of the invention will now be described withreference to the drawings.

[0039] First, referring to FIGS. 1a, 1 b and 2, a tripod type constantvelocity joint 11 is no different from the one shown in FIGS. 15 and 16described previously, as far as the basic arrangement is concerned,comprising a hollow cylindrical housing 14 fixed to the end of a firstrotary shaft 12, such as a driving shaft, and a tripod 16 fixed to theend of a second rotary shaft 13, such as the rotary shaft on the wheelside.

[0040] The housing 14, herein, is formed integrally with the firstrotary shaft 12, and has axially extending recessed grooves 14 a atcircumferentially trisectional positions on the inner peripheralsurface. Each recessed groove 14 a is recessed to extend radiallyoutward from the inner peripheral surface of the housing 14, and iscomposed of a pair of circumferentially opposed guide surfaces 14 b anda bottom surface positioned on the radially outside of the housing andconnecting the two guide surfaces 14 b. The pair of guide surfaces 14 bprovide a raceway for guiding an outer roller 26, to be later described,axially of the housing for rolling therein, and torque is transmittedbetween them and the outer roller 26. Further, part of the bottomsurface of the recessed groove 14 a is formed with guide shouldersurfaces 14 c for guiding the rolling of the outer roller 26. Theseguide shoulder surface 14 c perform the role of maintaining the postureof the outer roller 26 parallel with the housing axis when the outerroller moves in the recessed groove 14 a, ensuring smooth rolling.

[0041] The tripod 16 comprises a boss 16 a and a trunnion journal 16 b.The boss 16 a is fixed to the end of the second rotary shaft 13. Forexample, a spline shaft formed in the second rotary shaft 13 and splineholes formed in the boss 16 a fit together and are positioned by a stopring. The trunnion journals 16 b project radially from circumferentiallytrisectional positions on the boss 16 a. The end of each trunnionjournal 16 b is spherical.

[0042] Each trunnion journal 16 b supports a roller assembly 20. Theroller assembly 20 is of a double roller type consisting of an innerroller 22 and an outer roller 26 that are relatively turnable throughneedle rollers 24. The inner peripheral surface of the inner roller 22is a partial spherical inner peripheral surface having substantially thesame radius of curvature as that of the spherical outer peripheralsurface of the trunnion journal 16 b. The spherical inner peripheralsurface of the inner roller 22 is oscillably supported around theperiphery of the spherical outer peripheral surface of the trunnionjournal 16 b.

[0043] Needle rollers 24 are interposed between the cylindrical outerperipheral surface of the inner roller 22 and the cylindrical innerperipheral surface of the outer roller 26. Therefore, the inner andouter rollers 22 and 26 are capable of relative rotation and axialmovement. In order to prevent slipping-off of the needle rollers 24,needle roller retainers 26 a and 26 b are installed throughout thecircumference on both edge ends of the cylindrical inner peripheralsurface of the outer roller 26. As an example of a needle rollerretainer, there is shown a case in FIG. 1a, using a retainer 25 aseparate from the outer roller 26, and a stop ring 25 b, and FIG. 2shows another case where a retainer is integral with the outer roller26. As shown in FIG. 1b, which is a partial enlarged view of FIG. 1a,annular retainers 25 a are installed on both end sides of the needlerollers 24, and stop rings 25 b are mounted in stop ring grooves formedin the inner peripheral surface of the outer roller 26 at both ends.

[0044] The outer rollers 26 are received in the recessed grooves 14 a inthe housing 14. A pair of guide surfaces 14 b defining each recessedgroove 14 a each form substantially the same arc, in the cross-sectionof the housing 14, as the generating line of the outer peripheralsurface of the outer roller 26. Therefore, the outer roller 26 isrollably supported between these two guide surfaces 14 b.

[0045] During the use of the constant velocity joint constructed in themanner described above, for example, when the first rotary shaft 12 isrotated, the rotary force thereof is transmitted from the housing 14 tothe boss 16 a of the tripod 16 through the roller assemblies 20 (22, 24,26) and the trunnion journals 16 b to rotate the second rotary shaft 13.Further, in the case where the center axes of the first and secondrotary shafts 12 and 13 are out of alignment with each other, in otherwords, they take an operating angle therebetween, with the rotation ofthe two rotary shafts each trunnion journal 16 b is displaced in adirection to swing around the axis of the tripod 16 with respect to theguide surfaces 14 b of the corresponding recessed groove 14 a. At thistime, the outer roller 26 of the roller assembly supported by eachtrunnion journal 16 b rolls on the guide surfaces 14 b of the recessedgroove 14 a while being displaced axially of the trunnion journal 16 b.These movements, as is known in the art, secure equality of velocitybetween the first and second rotary shafts.

[0046] As shown at 16 c in FIG. 3, the outer diameter of the boss 16 ais heavily chamfered at one end surface (the left-hand side end surfacein FIG. 3) of the boss 16 a of the tripod 16. Thereby, the rollerassembly 20 can be greatly tilted when it is to be assembled to thetrunnion journal 16 b, and since interference is limited to only twoopposed places where the trunnion journal 16 b is subjected to a load,pushing in the inner roller 20 attended by elastic deformation makesassemblage possible. Flat surfaces may be provided for relief at twopositions (outside the loading range) at right angles with the positionwhere the trunnion journal 16 b is subjected to a load.

[0047] With the above construction, since torque is transmitted betweenspherical inner peripheral surface of the inner roller 22 and thespherical outer peripheral surface of the trunnion journal 16 b, thecontact surface pressure is kept low, which is advantageous from thestandpoint of strength and durability, making it possible to keep themajor diameter of the contact ellipse relatively small withoutincreasing rotation-directional play, and to decrease the spin moment onthe contact ellipse generated with the swing of the trunnion journal.Therefore, it is possible to avoid more contact than is necessarybetween the recessed groove 14 a in the housing 14 and the one guidesurface 14 c, and the rolling direction of the roller assembly 20 isstabilized, so that it becomes possible to provide a joint wherein therolling resistance in the roller assembly 20 is low and so is the axialforce. As described above, it becomes possible to provide a tripod typeconstant velocity joint ensuring the coexistence of low rollingresistance in the roller assembly and high strength and high durability.

[0048] Next, FIGS. 4a-4 c show modifications in which flat surfaces ordents 16 d are provided at or around the center position where thetrunnion journal 16 b is subjected to a load. Flat surfaces or dents ofoptional size are provided in a range where the contact area reduces to⅕ of the contact area by spherical fitting without flat surfaces ordents. The number of small flat surfaces or dents is not particularlylimited. FIG. 4a shows the case of using a single, FIG. 4b shows thecase of using four, and FIG. 4c shows the case of using a large number.In the case of providing a plurality, a suitable repetitive pattern orrandom dispersion may be employed. In the case of the embodiment shownin FIGS. 1a and 2, although the contact stress in the spherical fittingsection is small, the amount of relative slip in the center of thecontact ellipse is at a minimum, so that in the case of continuousrotation under a load for a long time, poor lubrication takes place,sometimes leading to a lowering in rotation durability. Themodifications shown in FIGS. 4a-4 c eliminate such drawbacks.

[0049] In a modification shown in FIG. 5a, both end edges of thecylindrical inner peripheral surface of the outer roller 26 are formedwith projections throughout the periphery to provide integrally formedneedle roller retainers 26 a and 26 b. This produces the effect ofreducing the number of parts. That is, as shown, integrally forming theinner needle roller retainer 26 a and the outer needle roller retainer26 b on the outer roller 26 makes it possible to constitute the rollerassembly by only three bodies, the inner roller 22, needle rollers 24and outer roller 26. It is also possible, however, to make either theinner needle roller retainer 26 a or the outer needle roller retainer 26b integral with the outer roller 26 while using a separate stop ring orthe like for the other.

[0050] A modification shown in FIG. 5b establishes the relation Di<dowhere Di is the inner diameter of the inner needle roller retainer 26 aon the cylindrical inner peripheral surface of the outer roller 26,i.e., at the joint inner diameter side end, the inner diameter of and dois the outer diameter of the inner roller 22. The relation Di<do ensuresthat, in the state of the tripod kit, i.e., in the unit state of thetripod 16 and the roller assemblies 20, the outer roller 26 is hardlydisassembled from the inner roller 22, and as can be understood fromFIG. 1a, even if the outer roller 26 moves downward, it interferes withthe boss 16 a of the tripod 16 to prevent the needle rollers 24 fromdisassembling; thus, handling is easy.

[0051] In a modification shown in FIG. 6a, both end edges of thecylindrical outer peripheral surface of the inner roller 22 are providedwith projections throughout the circumference to provide integrallyformed needle roller retainers 22 a and 22 b. This produces the effectof reducing the number of parts. That is, as shown, integrally formingthe inner needle roller retainer 22 a and the outer needle rollerretainer 22 b on the inner roller 22 makes it possible to constitute theroller assembly by only three bodies, the inner roller 22, needlerollers 24 and outer roller 26. In this case also, it is possible tomake either the inner needle roller retainer 22 a or the outer needleroller retainer 22 b integral with the inner roller 22 while using aseparate stop ring or the like for the other.

[0052] A modification shown in FIG. 6b establishes the relation Di<dowhere do is the outer diameter of the outer needle roller retainer 22 bon the cylindrical outer peripheral surface of the inner roller 22,i.e., the outer diameter of the joint outer diameter side end, and Di isthe inner diameter of the outer roller 26. The relation Di<do ensuresthat, in the state of the tripod kit, the outer roller 26 is hardlydisassembled from the inner roller 22, so that handling is easy.

[0053] Referring again to FIG. 17a, in the prior art joint shown in thisfigure, each trunnion journal 8 has two flat portions 8 a perpendicularto the axis z of the tripod 5. The radius r_(T) of the arc generatingthe spherical outer peripheral surface of the trunnion journal 8 issmaller than the radius of curvature, C/2, of the spherical innerperipheral surface of the inner roller 9 a. And the assembling of theinner roller 9 a to the trunnion journal 8 is effected by rotating thetripod 5 around the axis z of the inner roller 9 a by an angle α atwhich the inlet diameter B of the inner roller 9 a (smaller than theinner diameter C) is larger than or equal to a projection A (α) of thediameter A of the spherical outer peripheral surface of the trunnionjournal 8 onto this diameter. In the case of this conventional joint, asshown at 8 b in FIG. 17b, since a protuberant forged parting lineprojecting from the outer diameter surface of the trunnion journal 8 canbe positioned in the center of the load surface of the trunnion journal,a removing operation such as grinding is inevitable. In order to providea tripod type constant velocity joint ensuring the coexistence ofreduced shudder with the joint assembled to an automobile, highdurability and cost reduction, it is desired that no operation ofremoving the forged parting line of the trunnion journal be required andthat spherical fitting be made possible while holding small theclearance between the spherically surface-fitting inner roller andtrunnion journal.

[0054] Referring to FIGS. 7a-7 c, the outer peripheral surface of thetrunnion journal 16 b is spherical for spherical fitting to thespherical inner peripheral surface of the inner roller 22, but a relief16 a is partially formed along the forged parting line 16 p so that theprotuberance of the forged parting line 16 p inwardly recedes from thespherical outer peripheral surface so as not to project outward, asshown in broken line in FIG. 7c. Therefore, it becomes possible todispense with the step of removing the forged parting line 16 p, and touse the cold molded surface in its molded state, leading to costreduction. In this case, the relief 16 e portion cannot bear a load andhence the loading area is decreased; however, even if the loading rangeis partly decreased, a sufficient load capacity can be held because ofthe type in which the trunnion journal 16 b and the inner roller 22cooperate with each other to bear a load by spherical fitting of widerange. FIGS. 7a-7 c exemplify the case where the relief 16 e is a flatsurface, but a cylindrical surface or some other curved surface may beemployed. Further, in the case of providing the relief 16 e, as comparedwith the case of not providing the relief 16 e, the effect of reducingthe interference margin in assembling the inner roller 22 to thetrunnion journal 16 b is obtained, and the amount of elastic deformationof the inner roller 22 can be made small or eliminated.

[0055] Further, in this construction, the inner roller 22 is sphericallysurface-fitted on the trunnion journal 16 b and is integrally supportedaxially of the trunnion journal 16 b, so that its movement in thedirection of the axis of the trunnion journal accompanying rotation withan operating angle taken is allowed by rolling slip on the needlerollers 24 disposed between the inner and outer rollers 22 and 26;therefore, the internal friction force is low and a low rollingresistance in rollers is attained. In the case of the prior art shown inFIG. 17a, when the rollers are to be assembled to the trunnion journal,the rollers are tilted in a plane (corresponding to the plane of FIG.1a) orthogonal to the plane of FIG. 3. In order to make it possible togreatly tilt the rollers, it is necessary to reduce the outer diameterof the boss, that is, to reduce the thickness of the boss or to prolongthe underhead dimension of the trunnion journal. This, however, causesdrawbacks that if the outer diameter of the boss is reduced, the bossstrength lowers and that if the underhead dimension of the trunnionjournal is increased, the joint outer diameter increases. Thearrangement of FIGS. 7a-7 c avoids such drawbacks and makes it possibleto provide a tripod type constant velocity joint ensuring thecoexistence of all such factors as low rolling resistance, highstrength, high durability, and cost and size reduction for rollers.

[0056] Various concrete forms of the relief 16 e may be contemplated.The simplest example is shown in FIG. 8a wherein part of the sphericalis removed to provide a flat surface. In the case of providing a reliefby simply removing part of the spherical surface, however, the widthdimension A of the relief increases and the area to bear the loaddecreases. Thus, for example, as shown in FIGS. 9a-9 c, it is possibleto form a relief 16 e assuming an arcuate shape in the longitudinalsection of the trunnion journal 16 b. In this embodiment, there is anadvantage that the width dimension B of the relief is small while thearea to bear the load is large. However, both of these embodimentsresult in a contact state as shown in FIG. 8b, with a concentratedstress occurring in the edge, causing premature spalling. Forming acorner R at the edge may sometimes fail to be sufficiently effective.

[0057] What is shown in FIG. 10 is an arrangement wherein the outershape of the torque load region of the trunnion journal 16 b issubstantially double spherical. Concretely, the relation r/2<R<r isestablished where r is the radius of curvature of the spherical innerperipheral surface of the inner roller 22 and R is the radius of thedouble spherical surface of the trunnion journal 16 b. In this case, theparting line position recedes from the inner spherical surface of theinner roller toward the minor diameter side, so that a relief 16 e isformed without taking special measures. In a torque-loaded state, thecontact regions between the trunnion journal 16 b and the inner roller22 are located in two positions symmetrical with respect to the forgedparting line 16 p of the trunnion journal 16 b.

[0058] As shown in FIG. 11, dimensional setting may be such that with θ₁being an angle at which the inner roller 22 is about to separate fromthe trunnion journal 16 b when the inner roller 22 is being tilted withrespect to the trunnion journal 16 b, at the point of time when theinner roller 22 takes an angle θ₂ that is slightly smaller than θ₁, theouter roller 26 interferes with the second rotary shaft 4 or the stopring 4 a mounted on the second rotary shaft. Employing such arrangementensures that in the state of the unit consisting of the tripod 16 androller assemblies 20, that is, tripod kit, when the tripod 16 isassembled to the second rotary shaft 4 and the stop ring 4 a is mounted,the inner roller 22 interferes with the stop ring 4 a or the secondrotary shaft 4 and cannot tilt up to the angle θ₁ at which it separatesfrom the trunnion journal 16 b, so that the tripod kit (16, 20) and therotary shaft 4 assume a unit handling state, which greatly facilitateshandling.

[0059] In the prior art joint shown in FIG. 17a, the radius ofcurvature, r_(T), of the generating line of the trunnion journal 8 issmaller than the radius A/2 of the trunnion journal 8 so as to establishthe relation φA<φB when the rollers (9 a, 9 b) are tilted in thecircumferential direction of the joint with respect to the trunnionjournal 8, and spherical fitting is made possible by proving flatsurfaces 8 a. In this case, however, there are problems that the radiusof curvature, r_(T), of the trunnion journal 8 has to be decreased withrespect to the curvature of the inner spherical surface of the innerroller 9 a that spherically fits on the trunnion journal 8 and that thesurface pressure increases. The assemblage is made possible by settingthe spherical fitting clearance at a large value instead of by reducingthe radius of curvature, r_(T), of the trunnion journal 8. In this case,however, there is a problem that the rotation-directional play of thejoint increases. Further, since it is necessary to avoid interferencebetween the root of the trunnion journal disposed circumferentially ofthe joint subjected to a torque load and the roller, the enlargement ofthe underhead diameter of the trunnion journal is limited. Furthermore,in applying limit design for size and weight reduction, the root of thetrunnion journal disposed circumferentially of the joint subjected to atorque load probably becomes the lowest strength portion of the trunnionjournal, so that high strength is difficult to secure. Accordingly, in atripod type constant velocity joint of high durability type in whichsurface pressure is reduced by spherical fitting while keeping small theclearance between spherically surface-fitting inner roller and trunnionjournal to keep the rotation-directional play small, it is desired toachieve light-weight compaction and cost reduction while securing thetrunnion journal underhead strength.

[0060] Referring to FIGS. 12a and 12 b, the root of the trunnion journal16 b is of non-circular cross-section in which the diameter measuredcircumferentially of the joint is larger than the diameter measuredaxially of the joint. FIG. 12b shows an elliptic shape with its minoraxis directed axially of the joint as a typical example of anon-circular shape in which the diameter measured circumferentially ofthe joint is larger than the diameter measured axially of the joint.

[0061]FIG. 3 shows how to assemble the roller assembly 20 to thetrunnion journal 16 b. As shown at 16 c in this figure, only the side ofboss 16 a of the tripod 16 associated with the end of the second rotaryshaft 13 (left-hand side end in FIG. 3, right-hand side end in FIG. 2)is heavily chamfered, and the heavy chamfer functions as aninterference-avoiding relief between the trunnion journal 16 b and theroller assembly 20, making it possible to greatly tilt the rollerassembly 20 as shown in phantom line in FIG. 3 when the roller assembly20 is assembled to the trunnion journal 16 b. And since it is at onlytwo opposed places as seen in the torque load acting direction (thedirection perpendicular to the plane of the sheet of FIG. 3) that theinner roller 22 of the roller assembly 20 interferes with the trunnionjournal 16 b, assemblage is made possible by pushing in the inner roller22 while elastically deforming the same.

[0062] In addition, it is essential only that an interference-avoidingrelief between the trunnion journal 16 b and the roller assembly 20 bepresent in region of the underhead portion of the trunnion journaldisposed axially of the joint; such relief is unnecessary for the regionof the trunnion journal underhead portion disposed circumferentially ofthe joint. With this design specification, since aninterference-avoiding relief in the underhead circumferential positiontending to be the maximum stress position when subjected to torque loadis unnecessary, strength improvement becomes possible and it is possibleto provide a more compact tripod type constant velocity joint. Further,flat surfaces may be provided for relief at two places (outside the loadrange) at right angles with the position subjected to a torque load onthe trunnion journal 16 b.

[0063] According to the above construction, it is possible to provide atripod type constant velocity joint of high performance type, whereinsince torque is transmitted between the spherical inner peripheralsurface of the inner roller 22 and the spherical trunnion journal 16 b,the contact surface pressure is kept low, a fact which is advantageousfor strength and durability, while the underhead strength of thetrunnion journal 16 b is also improved, and high performance, highstrength, high durability, and compaction are all satisfied.

[0064] As shown in FIGS. 13, 14a, and 14 b, let θ be the angle at whichthe inner roller 22 is tilted when assembled to the trunnion journal 16b. Then, the maximum diameter φD of the trunnion journal 16 b includingthe protuberance maximum outer diameter portion of the forged partingline 16 d as projected in the direction of angle θ may be set smallerthan the fitting insertion side inner diameter θd of the inner roller22. Further, as shown in FIGS. 14a and 14 b, a notch is locally formedin the insertion side inner diameter of the inner roller 22. Let φd₂ theinner diameter of the notch, and φD₂ be the maximum diameter of thetrunnion journal 16 b (including the forged parting line 16 d) projectedin the direction of angle θ. Then, these factors may be set such thatφD₂<φd₂. Thereby, when the roller assembly 20 is to be assembled to thetrunnion journal 16 b, it is possible to do so without elasticallydeforming the inner roller 20. Therefore, it becomes possible todispense with the forged parting line removing step and thepressure-fitting step when the roller assembly 20 is assembled to thetrunnion journal 16 b.

What is claimed is:
 1. A tripod type constant velocity joint comprisinga hollow cylindrical housing fixed to the end of a first rotary shaftand formed with axially extending recessed grooves opened at one axialend and located at circumferentially trisectional positions on the innerperipheral surface, a tripod consisting of a boss fixed to the end of asecond rotary shaft, and end-spherical trunnion journals radiallyprojecting from circumferentially trisectional positions on the boss,roller assemblies each consisting of an inner roller swingably fitted atthe inner peripheral surface thereof on the spherical outer peripheralsurface of the trunnion journal, and an outer roller supported forrotation and axial movement on the outer peripheral surface of the innerroller through needle rollers, wherein the outer rollers are received inthe recessed grooves in the housing and are rollable axially of thehousing, each recessed groove consists of guide surfaces contacting theouter peripheral surface of the outer roller and subjected to loads, andguide shoulder surfaces for guiding the outer roller axially of thehousing, and only side of the outer diameter of said boss associatedwith the end of the second rotary shaft is heavily chamfered.
 2. Atripod type constant velocity joint as set forth in claim 1, whereinflat surfaces or dents are formed at load-imposed positions on thespherical outer peripheral surface of the trunnion journal.
 3. A tripodtype constant velocity joint as set forth in claim 1, wherein at leastone end of the inner peripheral surface of the outer roller isintegrally provided with a needle roller retainer.
 4. A tripod typeconstant velocity joint as set forth in claim 1, wherein at least oneend of the outer peripheral surface of the inner roller is integrallyprovided with a needle roller retainer.
 5. A tripod type constantvelocity joint as set forth in claim 1, wherein the inner diameter ofthe cylindrical inner peripheral surface of the outer roller at thejoint inner diameter side end is smaller than the outer diameter of theinner roller.
 6. A tripod type constant velocity joint as set forth inclaim 1, wherein the outer diameter of the cylindrical outer peripheralsurface of the inner roller at the joint outer diameter side end issmaller than the inner diameter of the outer roller.
 7. A tripod typeconstant velocity joint comprising a hollow cylindrical housing fixed tothe end of a first rotary shaft and formed with axially extendingrecessed grooves opened at one axial end and located atcircumferentially trisectional positions on the inner peripheralsurface, a tripod consisting of a boss fixed to the end of a secondrotary shaft, and end-spherical trunnion journals radially projectingfrom circumferentially trisectional positions on the boss, rollerassemblies each consisting of an inner roller swingably fitted at theinner peripheral surface thereof on the spherical outer peripheralsurface of the trunnion journal, and an outer roller supported forrotation and axial movement on the outer peripheral surface of the innerroller through needle rollers, wherein the outer rollers are received inthe recessed grooves in the housing and are rollable axially of thehousing, each recessed groove consists of guide surfaces contacting theouter peripheral surface of the outer roller and subjected to loads andguide shoulder surfaces for guiding the outer roller axially of thehousing, and a relief is locally formed along the forged parting line ofthe trunnion journal, thereby receding the protuberance of the partingline inwardly from the outer peripheral surface of the trunnion journal.8. A tripod type constant velocity joint as set forth in claim 7,wherein the outer diameter of the boss of the tripod at one axial endthereof is chamfered more heavily than at the other end thereof, therebypreventing the roller assembly from interfering with said boss when theroller assembly is tilted for assemblage to the trunnion journal.
 9. Atripod type constant velocity joint as set forth in claim 7, whereinwith θ being an angle at which the roller assembly is tilted forassemblage to the trunnion journal, the maximum diameter of the trunnionjournal including the forged parting line projected in the direction ofangle θ is not more than the inner diameter on the inner rollerinsertion side.
 10. A tripod type constant velocity joint as set forthin claim 7, characterized in that the setting is such that with θ₁ beingthe angle at which the roller assembly is about to separate from thetrunnion journal, the roller assembly interferes with the rotary shaftwhen it is tilted up to an angle θ₂ (θ₂<θ₁) after the rotary shaft hasbeen mounted in the tripod kit.
 11. A tripod type constant velocityjoint comprising a hollow cylindrical housing fixed to the end of afirst rotary shaft and formed at the inner peripheral surface thereofwith axially extending recessed grooves opened at one axial end andlocated at circumferentially trisectional positions on the innerperipheral surface, a tripod consisting of a boss fixed to the end of asecond rotary shaft, and end-spherical trunnion journals radiallyprojecting from circumferentially trisectional positions on the boss,roller assemblies each consisting of an inner roller swingably fitted atthe inner peripheral surface thereof on the spherical outer peripheralsurface of the trunnion journal, and an outer roller supported forrotation and axial movement on the outer periphery of the inner rollerthrough needle rollers, wherein the outer rollers are received in therecessed grooves in the housing and are rollable axially of the housing,each recessed groove consists of guide surfaces contacting the outerperipheral surface of the outer roller and subjected to loads, and guideshoulder surfaces for guiding the outer roller axially of the housing,it being arranged that when the roller assembly is to be assembled tothe trunnion journal, it is done so by tilting the roller assemblyaxially of the joint, the root of the tripod journal being ofnon-circular cross-section in which the diameter measuredcircumferentially of the joint is larger than the diameter measuredaxially of the joint.
 12. A tripod type constant velocity joint as setforth in claim 11, wherein the outer diameter of the boss of the tripodon the second rotary shaft end side is heavily chamfered.
 13. A tripodtype constant velocity joint as set forth in claim 11, wherein a reliefis locally formed along the forged parting line of the trunnion journal,so that the height of the parting line is not more than the sphericalsurface diameter.
 14. A tripod type constant velocity joint as set forthin claim 11, wherein the cross-section of the trunnion journal in thetorque load region is substantially double spherical.
 15. A tripod typeconstant velocity joint as set forth in claim 14, wherein the radius Rof the double spherical surface of the trunnion journal is set in therange r/2<R<r where r is the radius of curvature of the spherical innerperipheral surface of the inner roller.
 16. A tripod type constantvelocity joint as set forth in claim 11, wherein the setting is suchthat with θ₁ being the angle at which the roller assembly is about toseparate from the trunnion journal, the roller assembly interferes withthe rotary shaft when it is tilted up to an angle θ₂ (θ₂<θ₁) after therotary shaft has been mounted in the tripod kit.
 17. A tripod typeconstant velocity joint as set forth in claim 11, wherein at least oneend of the inner peripheral surface of the outer roller is integrallyformed with a needle roller retainer.
 18. A tripod type constantvelocity joint as set forth in claim 17, wherein the inner diameter ofthe cylindrical inner peripheral surface of the outer roller at thejoint inner diameter side end is smaller than the outer diameter of theinner roller.
 19. A tripod type constant velocity joint as set forth inclaim 11, wherein at least one end of the outer peripheral surface ofthe inner roller is integrally formed with a needle roller retainer. 20.A tripod type constant velocity joint as set forth in claim 19, whereinthe outer diameter of the cylindrical outer peripheral surface of theinner roller at the joint outer diameter side end is larger than theinner diameter of the outer roller.